In order to solve the problem that the flow characteristics of the plunger type balanced regulating valve designed by empirical formula deviate greatly from the expected straight line, a scheme for optimizing the spool structure of the plunger type regulating valve is put forward. The scheme takes the flow coefficient and the flow coefficient increment as the criteria for evaluating the linear fit degree, takes the experimental test as the premise and the numerical simulation as the main means to adjust and optimize the spool structure step by step, and verifies the rationality and accuracy of the scheme through numerical simulation. The results show that the optimized spool structure makes the flow characteristics highly fit the straight line, and the deviation of the flow coefficient from the theoretical value at each opening is reduced from more than 8% to less than 2%. The deviation of flow coefficient increment from the theoretical value before optimization is mostly more than 15%, and the maximum is up to63.26% decreased to less than 5%, and the maximum value was only 13.62%.

The spherical valve pair is one of the commonly used structures of high pressure and large flow piston pump with compact structure, large bearing area and strong ability to resist overturning moment. Its reliability evaluation is the key part of reliability of piston pump. A reliability evaluation method for fatigue crack and wear degradation of spherical valve pairs with a certain tilt Angle of plunger is proposed. The distribution model of the oil film of the spherical valve pair was established, and the pressure expression of the inner and outer sealing belt was obtained to realize the force analysis of the valve pair. Through ANSYS simulation model and analysis of the weak link of the cylinder block, the fatigue reliability analysis of the cylinder block is carried out based on Miner criterion. The wear reliability of spherical plate pair is calculated based on inverse Gaussian theory. Finally, fatigue reliability and wear reliability are combined to study the overall reliability. The results show that the weakest link of the spherical valve pair of the axial piston pump with inclined plunger is the sharp corner of the interface of high and low pressure cavity holes. Under the given stress condition, the survival rate is 50%, the lowest cycle times of the equipment is 4.839×109, and the life of the cylinder block is 31 839.52 h. The order of magnitude of the overall stress cycle is consistent with the order of magnitude of the cycle in fatigue and wear reliability, so the overall reliability is reduced when multiple reliability are combined.